Inertia switch device

ABSTRACT

Movement of an inertia mass (4) from a rest position as a result of acceleration or deceleration in excess of a given threshold value causes a hinge-like assembly (8) having two parts (9 and 10) to pivot between two overcenter positions on either side of a center position in which the two parts (9 and 10) occupy a common plane to thereby cause movable electrical contacts (14 and 15) forming part of the hinge-like assembly (8) to engage or separate from further electrical contacts (31 and 32).

TECHNICAL FIELD OF THE INVENTION

This invention relates to an inertia switch device and concerns such adevice for opening or closing electrical contacts in response to anacceleration or deceleration attaining a predetermined threshold value.

BACKGROUND ART

Devices of this kind are known in which an inertia mass, held in aninoperative position by a spring or magnet, is freed by an accelerationor deceleration of predetermined intensity to effect the opening orclosing of electrical contacts. However, the mechanism which is actuatedby the inertia mass to open or close the electrical contacts tends to bea complex mechanism having a relatively large number of parts.Therefore, not only do these parts have to be made to strictmanufacturing tolerances, thus adding to the cost of the inertia switchdevice, but also the reliability of the inertia switch device tends todecrease in proportion to the number of parts required. Moreover, thecomplexity of the mechanism adds to the bulk and weight of the device.

DISCLOSURE OF THE INVENTION

An object of the invention is to simplify the mechanism which isactuated by the inertia mass.

According to the present invention an inertia switch device comprises ahinge-like assembly arranged to pivot between two over-centre positionson either side of a centre position in which two parts of the hinge-likeassembly occupy a common plane, the hinge-like assembly either carryingor constituting a movable electrical contact which either engages or isseparated from a further electrical contact when the hinge-like assemblypivots from one over-centre position to the other, and an inertia masswhich is movable from a rest position when the device is subjected to anapplied acceleration or deceleration exceeding a threshold value tocause the hinge-like assembly to move from one over-centre position tothe other and operate the movable contact.

The inertia switch device may include resilient biasing means arrangedto urge the hinge-like assembly towards the two over-centre positions.The resilient biasing means may comprise a spring extending between thetwo parts of the hinge-like assembly.

The inertia mass may be arranged to strike the hinge-like assemblydirectly to cause the hinge-like assembly to move from one over-centreposition to the other.

Alternatively, the inertia mass may be arranged to strike a supportstructure on which the hinge-like assembly is mounted to cause thehinge-like assembly to move from one over-centre position to the other.The support structure may comprise a base having two upstanding membersprovided with slots in which the hinge-like assembly is mounted.

Preferably the inertia mass is a ball accommodated in a conical seatlocated below the hinge-like assembly. The inertia mass may includemagnetic material and be restrained in the rest position by theattraction of a permanent magnet.

Conveniently, the hinge-like assembly and the inertia mass may beenclosed by a housing which also accommodates the further electricalcontact.

A reset member may be arranged to return the hinge-like assembly fromone over-centre position to the other, and the reset member may bearranged to provide a visual indication that the movable contact hasbeen operated.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example,with reference to the accompanying drawings in which:

FIG. 1 is a front elevation, partly in section, of an inertia switchdevice in accordance with the invention with one part of a housingremoved;

FIG. 2 is a front elevation similar to FIG. 1 but with the electricalcontacts in a different position to that shown in FIG. 1;

FIG. 3 is a fragmentary front elevation of the hinge-like assembly shownin FIG. 1 but in the centre position;

FIG. 4 is a plan view of the hinge-like assembly shown in FIG. 1;

FIGS. 5 and 6 are plan views similar to FIG. 4 but with the fixedcontacts located in different positions;

FIG. 7 is a fragmentary front elevation of another hinge-like assembly;

FIG. 8 is a plan view of the hinge-like assembly shown in FIG. 7;

FIGS. 9 and 10 are plan views similar to FIG. 8 but with the fixedcontacts located in different positions;

FIG. 11 is a front elevation, partly in section of another inertiaswitch in accordance with the invention with one part of the housingremoved; and

FIG. 12 is an exploded perspective view of the hinge-like assembly shownin FIG. 11.

BEST MODES FOR CARRYING OUT THE INVENTION

Referring in the first instance to FIGS. 1 to 3, the inertia switchdevice comprises a housing 1 moulded from electrically insulatingmaterial and having two similar parts which fit together, of which onepart 2 is seen in the Figures. The housing 1 accommodates an inertiamass 4 in the form of a spherical steel ball which is normallyrestrained by a magnet 5 in a frusto-conical seat 6. The force exertedby the magnet 5 on the inertia mass 4 is such that it is overcome by theattainment of a predetermined threshold value of acceleration ordeceleration acting on the device and thus on the inertia mass 4. Whenthis threshold value is attained the inertia mass 4 moves upwards out ofthe seat 6.

Located above the inertia mass 4 is a hinge-like assembly 8 formed bytwo plates 9 and 10 of electrically conductive material such as brasspivotally connected together at mutually interfitting castellated edges11 and 12. The outer edges of the two plates, which extend parallel tothe interfitting edges 11 and 12, are turned over to form movableelectrical contacts 14 and 15 which co-operate with respective fixedelectrical contacts 16 and 17 mounted on opposite sides of thehousing 1. The fixed contacts 16 and 17 are anchored in respective slots18 and 19 in the sides of the housing 1 so that their upper endsnormally bear against the movable contacts 14 and 15 when the inertiamass 4 is restrained within the frusto-conical seat 6 by the magnet 5.The lower ends of the contacts 16 and 17 form respective terminals 21and 22 which are enclosed by a cover 23. The hinge-like assembly 8 isarranged to pivot between two over-centre positions on either side of acentre position shown in broken line in FIG. 1 in which the two plates 9and 10 occupy a common plane above and parallel to the rim 25 of thefrusto-conical seat 6. When in the lower of these over-centre positions,as seen in full line in FIG. 1, the hinge-like assembly 8 is urgedtowards the inertia mass 4 by a spring 26 anchored in holes in the twoplates 9 and 10. When in the upper of these over-centre positions, asseen in FIG. 2, the hinge-like assembly 8 is urged by the spring 26towards a reset plunger 27 slidably mounted in the top 28 of thehousing 1. The reset plunger 27 is surrounded by a shroud 29.

In use of the device in an electrical circuit to release theelectrically operated door locks of a vehicle such as an automobile, orto disconnect a source of electrical potential from an electricallyoperated fuel pump of a vehicle, the device is mounted in an uprightposition in the vehicle and the terminals 21 and 22 are connected in theelectrical circuit concerned. Initially the hingelike assembly 8 wouldbe in the position shown in full line in FIG. 1 so that the fixedcontacts 16 and 17 are electrically interconnected by the movablecontacts 14 and 15 and the plates 9 and 10. Although the term "fixedcontacts" has been used in the foregoing description it will beappreciated that the inherent resilience of the contacts 16 and 17allows sufficient movement to provide adequate contact pressure at alltimes.

If the vehicle is involved in an accident so that an acceleration ordeceleration above the predetermined threshold value is applied to thedevice then the inertia mass 4 will ride up the frusto-conical seat 6and strike the underside of the hinge-like assembly 8. The impact of theinertia mass 4 with the plates 9 and/or 10 causes the plates to moveupwards beyond the centre position shown in broken line in FIG. 1 andinto the position shown in full line in FIG. 2. The spring 26 retainsthe hinge-like assembly 8 in this position so that the movable contacts14 and 15 are separated from the fixed contacts 16 and 17 and theelectrical circuit is broken. At the same time the reset plunger 27 ismoved upwards so that its upper end projects out of the shroud 29 thusproviding a visual indication that the electrical circuit has beenbroken.

The device can be reset by depressing the reset plunger 27 into theshroud 29 thus returning the hinge-like assembly 8 to its originalover-centre position as shown in full line in FIG. 1 with the movablecontacts 14 and 15 in engagement with the fixed contacts 16 and 17. Thusthe electrical circuit can be re-connected as and when required.

While the fixed contacts 16 and 17 would usually be located midway alongthe movable contacts 14 and 15 as shown in FIG. 4, they can equally wellbe located in the positions shown in FIGS. 5 and 6. Moreover, while thefixed and movable contacts shown in FIG. 1 to 6 are normally closedcontacts which open on impact the fixed and movable contacts couldequally well be normally open contacts which close on impact. As shownin FIGS. 7 and 8 the hinge-like assembly 8 is arranged so that themovable contacts 14 and 15 are normally separated from the fixedcontacts 16 and 17. FIGS. 9 and 10 show alternative positions for thefixed contacts 16 and 17.

Turning now to FIG. 11 and 12, the inertia switch device comprises ahousing 1 moulded from electrically insulating material having twosimilar parts which fit together of which one part 2 is shown in theFigures. As before the housing 1 accommodates an inertia mass 4 in theform of a spherical steel ball which is normally restrained in afrusto-conical seat 6 by a magnet 5.

Located above the inertia mass 4 is a hinge-like assembly 8 formed bytwo plates 9 and 10 of brass which are pivotally connected together atmutually interfitting edges 11 and 12. The outer edges of the two plateswhich extend parallel to the interfitting edges 11 and 12 are bent intoa sinuous shape to form movable contacts 14 and 15 which cooperate withrespective fixed electrical contacts 16 and 17 and also with fixedelectrical contacts 31 and 32 in a change-over contact assembly.

The hinge-like assembly 8 is supported for pivotal movement in a supportstructure 34 of electrically insulating material comprising a circularbase 36 and two substantially U-shaped members 37 upstanding from thebase 36. Projecting ears 38 at either side of the two plates 9 and 10rest within the slots 40 between the two arms of the U-shaped members 37which act as guides for the ears 38 to allow pivotal movement of thehinge-like assembly 8 between its two over-centre positions. Thehinge-like assembly 8 is urged towards these over-centre positions by ahelical spring 41 having its ends anchored in holes 42 in the plates 9and 10.

The fixed contacts 16 and 17 are anchored in respective slots 18 and 19in the sides of the housing 1 and their respective upper ends 43 and 44are bent horizontally so that they overlie the movable contacts 14 and15. The lower ends of the fixed contacts 16 and 17 form respectiveterminals 21 and 22. The fixed contacts 31 and 32 are also anchored inthe housing 1 and have upper ends 46 and 47 which are bent horizontallyso that they lie below the movable contacts 14 and 15 and have lowerends which form terminals 48 of which one is shown. A reset plungerslidably mounted in the top 28 of the housing 1 is surrounded by ashroud 29. Two horizontally extending abutments 49 at the lower end ofthe reset plunger 27 act as stop members to limit the upward movement ofthe reset plunger 27.

In use of the device in an electrical circuit to release theelectrically operated door locks of a vehicle and to disconnect a sourceof electrical potential from an electrically operated fuel pump of thevehicle the device is mounted in an upright position in the vehicle. Thenormal closed part of the change-over contacts are connected to theelectrical circuit for the fuel pump by means of terminals 48 while thenormally open part of the change-over contacts are connected to theelectrical circuit for the door locks by means of the terminals 21 and22.

If the vehicle is involved in an accident so that an acceleration ordeceleration above the predetermined value is applied to the device thenthe inertia mass 4 will ride up the frusto-conical seat 6 and strike theunderside of the circular base 36. The impact of the inertia mass 4 onthe base 36 moves the hinge-like assembly 8 upwards and causes the plate9 and 10 to move into the other over-centre position thus moving themovable contacts 14 and 15 away from fixed contacts 16 and 17 and intoengagement with fixed contacts 31 and 32. The electrical circuit for thefuel pump is broken and the electrical circuit to operate the door locksis energised. At the same time the reset plunger 27 is moved upwards sothat its upper end projects out of the shroud 29 thus providing a visualindication that the change-over contact assembly has bee operated.

The device can be reset by depressing the reset plunger 27 into theshroud 29 thus returning the hinge-like assembly 8 to its originalover-centre position with the movable contacts in engagement with thefixed contacts 16 and 17 and separated from the fixed contacts 31 and32.

While the inertia mass 4 in the embodiments of the invention describedabove is constituted by a spherical steel ball in a frusto-conical seat,since this form of inertia mass will respond to impact in any directionin a horizontal plane, in other embodiments of the invention other formsof inertia mass may be utilized. Moreover, although the inertia mass 8is restrained by a magnet 5 in the embodiments of the inventiondescribed above, in other embodiments of the invention the inertia massmay be restrained by springs or other suitable means.

We claim:
 1. An inertia switch device comprising:an inertia mass (4)which is movable from a rest position when the device is subjected to anapplied acceleration exceeding a threshold value; spaced electricalcontact means (16 and 17, and 31 and 32); a hinge-like assembly (8)which is mounted independently of the inertia mass (4) and in which twoparts (9 and 10) are connected for movement between two over-centrepositions on opposite sides of a centre position in which the two parts(9 and 10) are aligned with a common plane, in response to movement ofthe inertia mass (4) when subjected to said applied acceleration; andmovable electrical contact means (14 and 15) on at least part of thehinge-like assembly (8) and arranged to engage the spaced electricalcontact means (16 and 17, and 31 and 32) when the hinge-like assembly(8) is in one of the over-centre positions; characterized in that: thespaced electrical contact means (16 and 17, and 31 and 32) comprise twofirst contacts (16 and 17); the movable electrical contact meanscomprise two electrically connected movable contacts (14 and 15); thehinge-like assembly (8) is mounted independently of the spacedelectrical contact means (16 and 17, and 31 and 32) so that the movablecontacts (14 and 15) are respectively movable into and out of contactwith the two first contacts (16 and 17) so as to bridge the first twocontacts (16 and 17); and resilient biasing means (26 or 41) areoperable, on said movement of the inertia mass (4), to move thehinge-like assembly (8) from said one of the overcentre positions, inwhich the movable electrical contacts (14 and 15) engage the firstelectrical contacts (16 and 17, and 31 and 32), to the other of theover-centre positions, and are operable to releasably hold thehinge-like assembly (8) in said other of the over-centre positions. 2.An inertia switch device, as claimed in claim 1, wherein the spacedelectrical contact means (16 and 17, and 31 and 32) comprise two firstfixed contacts (16 and 17) and two second fixed contacts (31 and 32);the hinge-like assembly (8) is mounted between the two first fixedcontacts (16 and 17) and between the two second fixed contacts (31 and32) so that the movable contacts (14 and 15) are respectively movableout of contact with the two second fixed contacts (31 and 32) and intocontact with the two first fixed contacts (16 and 17) so as to bridgethe two first fixed contacts (16 and 17) and are respectively movableout of contact with the two first fixed contacts (16 and 17) and intocontact with the two second fixed contacts (31 and 32) so as to bridgethe two second fixed contacts (31 and 32).
 3. An inertia switch device,as claimed in claim 1, wherein the resilient biasing means (26 or 41)comprise a spring extending between the two parts (9 and 10) of thehinge-like assembly (8).
 4. An inertia switch device, as claimed inclaim 1, wherein the inertia mass (4) is arranged to strike thehinge-like assembly (8) directly to cause the hinge-like assembly (8) tomove from one over-centre position to the other.
 5. An inertia switchdevice, as claimed in claim 1, wherein the inertia mass (4) is arrangedto strike a support structure (34) on which the hinge-like assembly (8)is mounted to cause the hinge-like assembly (8) to move from oneover-centre position to the other.
 6. An inertia switch device, asclaimed in claim 5, wherein the support structure (34) comprises a base(36) having two upstanding members (37) provided with slots (40) inwhich the hinge-like assembly (8) is mounted.
 7. An inertia switchdevice, as claimed in claim 1, wherein the inertia mass (4) is a ballaccommodated in a conical seat (6) located below the hinge-like assembly(8).
 8. An inertia switch device, as claimed in claim 1, wherein theinertia mass (4) includes magnetic material and is restrained in therest position by the attraction of a permanent magnet (5).
 9. An inertiaswitch device, as claimed in claim 1, wherein the hinge-like assembly(8) and the inertia mass (4) are enclosed by a housing (1) which alsoaccommodates the spaced electrical contact means (16 and 17, and 31 and32).
 10. An inertia switch device, as claimed in claim 1, wherein areset member (27) is arranged to return the hinge-like assembly (8) fromone overcentre position to the other.
 11. An inertia switch device, asclaimed in claim 10, wherein the reset member (27) is arranged toprovide a visual indication that the movable contact (14 and 15) hasbeen operated.